Known heat exchangers typically include a valve, the position of which regulates the amount of coolant flowing to the heat exchanger to control the temperature of the cooled substance output from the exchanger. Although the response times of the valve and system for controlling the valve are often critical, the response times may vary greatly over the operating range of the system. Known control systems are typically designed to maintain stability when the system is operating under the worst conditions for system stability, such as when the system has a high gain and a fast response time. When the system gains are low, however, the response times of such control systems are very slow which is undesirable for applications where a prompt response is critical.